A critical gap exists in our knowledge of the cellular interactions occuring during the morphological development of the olfactory system. Numerous behavioral and physiological studies have demonstrated the early functional capacities of the neonatal olfactory system. These include the ability to make olfactory discriminations in the neonate in addition to the detection of pheromonal cues which direct suckling behavior. Regional variation in the timecourse of functional development within the olfactory bulb has led to the suggestion that neuronal morpho- and synaptogenesis is regionally heterogeneous. Furthermore, that subpopulations of olfactory bulb neurons form parallel circuits that mature along different timecourses and thus process olfactory information during different periods of development. However, insufficient data exists to empirically evaluate these hypotheses at the morphological level. Consequently, this proposal seeks to provide information on several important issues. First, utilizing light microscopy, the morphological development of individual populations of neurons will be examined within different regions of the olfactory bulb. Second, utilizing electronmicroscopy, the fine structural maturation and synaptogenesis of olfactory circuits will be regionally examined. Third, a combined electronmicroscopy/Golgi procedure will be employed to study the maturation and synaptogenesis of identified neurons, including mitral, external tufted, middle tufted, deep tufted, superficial granule and deep granule. These analyses will test two important hypotheses: (1) there occurs in the olfactory system significant regional variation in the timecourse of morphological development and synaptogenesis; and (2) within the regional variation of development there exists further heterogeneity between local circuits comprised of mitral cells and the subpopulations of tufted cells. Addressing these questions will provide knowledge essential for resolving the controversy surrounding the functional capacities of the perinatal olfactory system. Moreover, information important for understanding cellular interactions which occur during development will be obtained as well as insights into the factors which influence the formation of discrete local circuits between identified neurons. Finally, the data will be relevant to issues of human development and health care such as olfactory guided nutritive behavior in the term and preterm infant. In utero olfactory function, and stimulation-induced modifications of prenatal and postnatal neurogenesis.